U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY INTERPRETIVE GEOLOGIC CROSS SECTIONS FOR THE DEATH VALLEY REGIONAL FLOW SYSTEM AND SURROUNDING AREAS, NEVADA AND CALIFORNIA By Donald S. Sweetkind1, Robert P. Dickerson2, Richard J. Blakely3, and Paul D. Denning1 2001 Prepared in cooperation with OFFICE OF ENVIRONMENTAL RESTORATION AND WASTE MANAGEMENT, U.S. DEPARTMENT OF ENERGY NATIONAL NUCLEAR SECURITY ADMINISTRATION NEVADA OPERATIONS OFFICE, under Interagency Agreement DE-AI08-96NV11967 1U.S. Geological Survey, Denver, Colo. 2Pacific Western Technologies, Inc., Denver, Colo. 3U.S. Geological Survey, Menlo Park, Calif. Pamphlet to accompany MISCELLANEOUS FIELD STUDIES MAP MF–2370 CONTENTS Abstract ......................................................................................................................................... 1 Introduction ................................................................................................................................... 1 Methodology ................................................................................................................................. 1 Stratigraphic overview .................................................................................................................... 3 Structural overview ........................................................................................................................ 6 Cross sections in the vicinity of the Nevada Test Site .................................................................... 8 Pre-Tertiary Structure of the Nevada Test Site area ................................................................... 8 Geology of the southwestern Nevada volcanic field (SWNVF) ................................................... 10 Geology of the eastern Nevada Test Site ................................................................................. 11 Geology of Yucca Mountain and the Crater Flat basin .............................................................. 12 Geology of Bare Mountain and Oasis Valley ............................................................................. 13 Cross sections in the vicinity of the Spring Mountains, Pahrump Valley, and the Amargosa Desert 14 Pre-Tertiary structure .............................................................................................................. 14 Tertiary extension west of the Spring Mountains ..................................................................... 15 Strike-slip faults in Pahrump Valley and the Amargosa Desert .................................................... 17 Cross sections in the vicinity of Death Valley ............................................................................... 18 Grapevine/ Funeral Mountains block ......................................................................................... 18 Northern Death Valley and Grapevine Canyon area .................................................................. 19 Central Death Valley volcanic/plutonic field and the Furnace Creek basin ................................... 19 The Black Mountains ............................................................................................................... 20 The Panamint Mountains ......................................................................................................... 21 Cross sections to the east of the Nevada Test Site ...................................................................... 21 Acknowledgments ........................................................................................................................ 23 References cited ........................................................................................................................... 23 i FIGURES 1. Map showing general geographic regions discussed in the text ................................................... 2 2. Location of cross section lines ........................................................................................ Sheet 1 3. LANDSAT mosaic showing cross section lines ................................................................ Sheet 1 4. Index map of place names and cross section lines ............................................................. Sheet 1 5. Geologic map showing cross section lines ....................................................................... Sheet 1 6. Thickness of Cenozoic basin fill and location of cross section lines ................................... Sheet 1 7. Index map of geologic structures and cross section lines .................................................. Sheet 1 8. Correlation diagram of thrust faults in the vicinity of the Spring Mountains, Pahrump Valley and the Amargosa Desert .................................................................................................... 16 CROSS SECTIONS H-1 to H-5, H-13 to H-16, and H-23 to H-28 ....................................................................... Sheet 2 H-6 to H-12 and H-17 to H-22 ............................................................................................. Sheet 3 ii ABSTRACT impacts to farming communities and endangered species habitat near discharge areas and wells in the This report presents a network of 28 geologic flow system. cross sections that portray subsurface geologic This report presents a series of deep, inter­ relations within the Death Valley regional ground- pretive geologic cross sections that transect the area water system, a ground-water basin that encom­ of the Death Valley ground-water flow system. The passes a 3° x 3° area (approximately 70,000 km2 ) in area of investigation covers approximately 70,000 southern Nevada and eastern California. The cross km 2 (latitudes 35°30’ to 37°45’ N., longitudes 115° sections transect that part of the southern Great to 117°45’ W.). The purpose of this network of Basin that includes Death Valley, the Nevada Test cross sections is to provide the structural and strati- Site, and the potential high-level nuclear waste un­ graphic framework of the region as a component of derground repository at Yucca Mountain. The spe­ USGS numerical modeling of regional ground-water cific geometric relationships portrayed on the cross flow in the region. These sections are intended to sections are discussed in the context of four general serve as the fundamental basis for the construction of sub-regions that have stratigraphic similarities and a three-dimensional digital hydrogeologic framework general consistency of structural style: (1) the model that itself provides the primary geometric ba­ Nevada Test Site vicinity; (2) the Spring Mountains, sis for subsequent numerical analysis of the regional Pahrump Valley and Amargosa Desert region; (3) the ground-water flow system. Similar networks of Death Valley region; and (4) the area east of the cross sections have been developed (Grose, 1983; IT Nevada Test Site. Corp., 1996) for recent three-dimensional numerical The subsurface geologic interpretations por­ models of the regional ground-water flow system (IT trayed on the cross sections are based on an integra­ Corp., 1996; D’Agnese and others, 1997). The grid tion of existing geologic maps, measured strati- of geologic sections that is contained in this report graphic sections, published cross sections, well data, provides a basis for comparison with existing three- and geophysical data and interpretations. The esti­ dimensional framework models (IT Corp., 1996; mated top of pre-Cenozoic rocks in the cross sec­ D’Agnese and others, 1997), and should guide future tions is based on inversion of gravity data, but the revisions of the three-dimensional geologic frame- deeper parts of the sections are based on geologic work model linked to the ground-water flow and conceptual models and are more speculative. radionuclide transport models. The region transected by the cross sections The locations of the individual cross sections includes part of the southern Basin and Range are presented on a 1:1,500,000-scale index map Province, the northwest-trending Walker Lane belt, (fig. 2) as well as on 1:750,000-scale maps of the Death Valley region, and the northern Mojave LANDSAT imagery (fig. 3), regional place names Desert. The region is structurally complex, where a (fig. 4), regional geology (fig. 5; after Faunt and locally thick Tertiary volcanic and sedimentary section others, 1997), regional gravity data processed as unconformably overlies previously deformed depth to Paleozoic basement (fig. 6; after Blakely Proterozoic through Paleozoic rocks. All of these and others, 1999), and general tectonic features of rocks have been deformed by complex Neogene ex- the region (fig. 7; after Grose and Smith, 1989). tensional normal and strike-slip faults. These cross The cross sections themselves are shown on sheets 2 sections form a three-dimensional network that por­ and 3. The cross sections are portrayed at trays the interpreted stratigraphic and structural rela­ 1:250,000 scale, and are accompanied by tions in the region; the sections form part of the geo­ 1:100,000-scale enlargements of certain areas logic framework that will be incorporated in a com­ requiring a larger scale to portray geologic detail. plex numerical model of ground-water flow in the The explanatory text that follows discusses the Death Valley region. specific geometric relationships portrayed on the cross sections in the context of four general sub-re­ INTRODUCTION gions (fig. 1) that have stratigraphic similarities and general consistency